Correction of cardiac output obtained by Modelflow® from finger pulse pressure profiles with a respiratory method in humans

The beat-by-beat non-invasive assessment of cardiac output (Q’, litre·min-1) based on the arterial pulse pressure analysis called Modelflow® can be a very useful tool for quantifying the cardiovascular adjustments occurring in exercising humans. Q’ was measured in nine young subjects at rest and during steady-state cycling exercise performed at 50, 100, 150 and 200 W by using Modelflow® applied to the Portapres® non-invasive pulse wave (Q’ Modelflow) and by means of the open-circuit acetylene uptake (Q’C2H2 Q values were correlated linearly (r = 0.784), but Bland–Altman analysis revealed that mean Q’Modelflow – Q’C2H2 difference (bias) was equal to 1.83 litre · min-1 with an S.D. (precision) of 4.11 litre · min-1, and 95 % limits of agreement were relatively large, i.e. from - 6.23 to + 9.89 litre · min-1. Q’ Modelflow values were then multiplied by individual calibrating factors obtained by dividing Q’C2H2 by Q’Modelflow for each subject measured at 150 W to obtain corrected Q’ Modelflow (Q’ corrected)values. Q’ corrected valueswerecomparedwiththecorresponding Q’ C2H2values, with values at 150 W ignored. Data were correlated linearly (r = 0.931) and were not significantly different. The bias and precision were found to be 0.24 litre · min-1 and 3.48 litre · min-1 respectively, and 95 % limits of agreement ranged from - 6.58 to + 7.05 litre · min-1. In conclusion, after correction by an independent method, Modelflow® was found to be a reliable and accurate procedure for measuring Q’ in humans at rest and exercise, and it can be proposed for routine purposes.